Some information taken from http://iggy.loyola.edu/1mr/revwar/history.html
Volunteer infantry regiment formed in Maryland (go figure), originally to fight in the American Revolution. Sometimes called the "Bayonets Of The Revolution", as they were the first troops of the Continental Army to use bayonet against the British; this was during the Battle Of Long Island, in which the 1st Maryland covered George Washington's retreat while suffering heavy casualties. Later participated in the attack on Stoney Point Fort, which was taken entirely by bayonet.
During the War Between The States, some 1st Marylanders joined the Union army, and some the Confederate. It is said that at some battles former comrades-in-arms found themselves fighting each other. After the end of the war, the 1st Maryland was reconstituted under a new insignia: a yin-yang in blue and gray.
The 1st Maryland eventually was incorporated into the 29th Infantry Division of the Maryland National Guard, still under the yin-yang. They participated in the Normandy landings on D-Day, where they were some of the first to hit the beach.
I pass by their headquarters almost every day; it is barely a block from my house in downtown Baltimore.